It is claimed by the inventor (Dr. Ramesh Chandra Gupta, Ph. D., P.E.) that with the use of expandable jacket around the soil specimen, uniform increase in diameter of soil specimen shall occur through its height without any localized bulging, permitting accurate calculation of new area of cross-section at any instant of time, when axial vertical load is applied during the triaxial compression test. New area of cross-section is required to calculate the deviator stress during process of shearing at any instant of time.
The triaxial compression test is considered to simulate in-situ conditions of a soil element at any depth below the ground surface. Lateral pressure applied in the triaxial chamber is generally kept approximately equal to in-situ horizontal stress from where the soil sample is extracted. It is a standard test for determination of strength and volume change characteristics of soils, (ASTM Designation: D4767-11, ASTM Designation: D2850). When vertical load is applied to any soil element located at certain depths, the soil element experiences vertical displacement with simultaneous lateral displacement. The ratio of lateral strain with axial (vertical) strain is governed by the Poisson's ratio of soil. The soil element at deeper depths does not or cannot experience non-uniform lateral displacement or localized bulging due to lateral uniform elastic restraint provided by the adjoining soil. Volume change in soil element depends on both vertical displacement and lateral displacement. Thus any determination of volume change from triaxial compression test where soil specimen undergoes non-uniform lateral displacement, (very often with localized bulging), does not or cannot be considered to accurately represent the actual volume change of soil elements insitu with increase in the vertical load.
To solve these problems and to accurately simulate insitu conditions, an expandable jacket as explained and detailed below, is being introduced in this invention to maintain uniform cross-section of the soil specimen without any possibility of localized bulging. From the triaxial compression tests, it has been established that loose or soft soils decrease in volume and very stiff to hard or dense to very dense soil increase in volume or dilate during process of shearing, however this research is based on tests when soil specimen experienced non-uniform lateral displacement along with probable localized bulging. After eliminating non-uniform lateral displacement of the specimen by use of expandable jacket, it shall be possible to re-review or re-check or confirm whether loose or soft soils shall continue to experience decrease in volume; and dense to very dense or very stiff to hard soils shall continue to experience increase in volume (dilation) during the process of shearing in the triaxial compression tests.